Key moments in humanity’s early and more recent history remain written in our DNA

Two new studies illuminate long standing mysteries in our evolutionary and cultural history.  Why were early humans smarter and more adaptable than our Neanderthal cousins even though their brains were about the same size?  When and where did the earliest Indo-European languages emerge leading to what about half the world speaks today?  DNA is a language all its own, but increasingly we are finding our story written inside of us.

The explosion of inexpensive DNA analysis technology and new techniques to harvest workable strands from specimens thousands and even tens of thousands of years old continues to illuminate parts of history that once seemed forever hidden.  It’s as if scientists were able to read the story of us encoded in our genes, solving long standing mysteries and illuminating key aspects of our evolution and culture.  Neanderthals, for example, emerged hundreds of thousands of years earlier than our own species, Homo sapiens.  The oldest known fossils date back some 430,000 years, though some experts believe they walked the earth for almost twice that long.  They were a tough and hardy people, with heavier builds than humans and strong bones.  Contrary to their depiction in popular culture as “cro magnon man,” they were also culturally and technologically advanced for their day.  They made tools, controlled fire and cooked, heated their caves with a hearth, wore clothing, and likely had some form of language and the beginnings of religious beliefs.  Neanderthals lived in small groups of ten to thirty individuals and adopted the lifestyle of a primitive hunter and gatherer, but they were also artists and explorers in their own right.  They gathered and wore trinkets for decorative purposes, painted the insides of their caves, and possibly played music.  Between 200,000 and 150,000 years ago, Neanderthals navigated the Ionian Sea, visiting Greek islands including Crete, Cephalonia, and Zakynthos.  Evidence suggests they traveled back and forth to mainland Europe regularly in reed boats.  Neanderthals also treated their sick and injured, including the use of splints to tend broken bones and medicinal plants, all tens, if not hundreds of thousands of years, before our own species fully emerged.

About 40,000 years ago, however, around the time humans around in Europe, the Neanderthals suddenly disappeared. For decades, evolutionary biologists have debated how our own species could have arisen so quickly and ultimately outcompeted our cousins so effectively in such a short period.  The dates are not precisely known for sure, but it appears that only a few millennia after we arrived in Europe around 45,000 years ago, Neanderthals went extinct.  The figure could be as low as 3,000 years of both species existing side by side.  The mere blink of an eye in evolutionary terms, especially considering Neanderthals roamed the earth for so long without us.  It has long been believed that something about our unique cognitive ability gave us a competitive edge.  The way this line of thinking goes, we were smarter, more creative, and more adaptable than our cousins.  By the time humans migrated to Europe, we’d already invented the bow and arrow, a powerful weapon and a significant advantage for any species that relies on hunting for food.  We also used special devices that throw spears further and harder than with our bare hands.  Homo sapiens has always been marked by an explosion of new ideas and inventions, even at this early stage.  Neanderthal culture, though advanced in its own right, moved much more slowly by comparison, unchanging for tens of thousands of years.  The challenge for proponents of the view that humanity’s advanced cognition ultimately enabled us to outcompete our cousins  has always been a simple one:  Neanderthals appear to have brains at least our size or even slightly larger.

The correlation between brain size and intelligence has been known since at least Charles Darwin.  The more brain cells a being has, the more “space” they have for thinking, memory, and ideas.  The evolution of the Homo line down to Homo sapiens has generally been marked by increased brain size at every step of the way.  The proto-human, Homo habilis, lived between 2.3 and 1.5 million years ago, and had a brain size averaging between 500 to 800 cubic centimeters.  In the intervening years, Homo sapien brain size doubled, increasing to between 1,400 and 1,500 cubic centimeters, but Neanderthals have always been in the same range, not smaller enough to impart any obvious deficiency.  What mechanism then could make us smarter and more adaptable enough to outcompete an ancient race in a mere handful of years?

Breakthrough research might well have found the answer.  A new study suggests that a change to a single amino acid in one of our metabolic genes causes our brains to develop more neurons than any other animal. In 2016, Wieland Hunter, a neurologist at the Max Planck Institute of Molecular Biology identified a mutation in the ARHGAP11B gene that was found in humans, Neanderthals, and another set of cousins, Denisovans, but not other primates.  The mutation increased the production of neurons in these species, accounting for an increase in a cognitive ability beyond the rest of our family tree, but not specific to the Neanderthals versus humans debate.  Next, Dr. Hunter studied the TKL1 gene, which differs between humans, Neanderthals, and (we believe) all other mammals by a single amino acid.  Dr. Hunter and his team were able to insert both versions of this gene into mice and observe the impact on development.  Sure enough, mice with the human version of the gene developed more basal radial glia, which ultimately developed into more cortical neurons.  The researchers also wondered if this gene could impact the folding of neurons in the brain, packing more brain matter into a smaller space.  The team repeated the experiment on ferrets, which have folds in their brain unlike mice, and the human version of the gene produced both more neurons and more folds, increasing cognitive capacity both by the number of “processors” available and how many of them could fit inside a skull.  To be sure, the team checked these findings against lab grown human specimens and the result was the same:  Tissue that grew with the human gene activated produced more cells that would become neurons than without it.  They also considered what this gene might be doing to have such a dramatic effect.  TKTL1 encodes an enzyme that increases the production of fatty acids.  Enzymes are evolution’s multiplier effect.  They do not create anything on their own, but they speed up other reactions and processes, sometimes by orders of magnitude.  The increased production of fatty acids appears to allow the progenitor cells to grow faster and divide more frequently during development, squeezing significantly more processing power out of the same raw materials, a classic enzyme effect.

Scientists are calling this discovery a breakthrough, especially in light of other recent studies that have helped map out the process for building a human brain.  It “is really a breakthrough,” explains Brigitte Malgrange, a developmental neurobiologist at the University of Liège, not involved in the study. “A single amino acid change is really, really important and gives rise to incredible consequences regarding the brain.”  Another scientist, Alysson Muotri, a neuroscientist at the University of California, San Diego, School of Medicine, referred to it as a “a tour de force.”  A “completely new … smoking gun,” exclaimed Christoph Zollikofer, a paleoanthropologist at the University of Zürich.  I would add:  As incredible as it sounds, this should not be surprising.  Evolution only functions one gene at a time, but once the basics of a body plan are in place, a single change to one of the genes that orchestrates or enhances the development process of an organism can have huge ramifications for the final product.  Neanderthals are believed to have been close enough to us genetically that populations were able to interbreed, and their DNA lives on in us to this day.  This implies that any genetic differences are likely to be very small, though certainly by being small that doesn’t make them incredibly important.

Fast forward thirty thousand years and genetic analysis is also helping tell the story of early human culture.  There is perhaps nothing more important to culture than language – the words we use in the songs we sing, the stories we tell, the poems we write, the other people we inspire, the business we conduct, the groups we organize, the adventures we plan and undertake.  Starting around 10,000 AD, humanity had begun to develop early civilizations and the languages we still use today were present in an ancestral form.  What linguists refer to as the “Indo-European” language family is spoken by about half the current world population.  The earliest form of this language is believed to have arisen in the flat plains that link Europe and China, known as the Eurasian Steppe, around 3,000 years ago during the Bronze Age.  Pastoral cultures were known to have populated this region dating back at least 5,000 years. Scientists refer to these people as the Yamnaya, literally “culture of pits” for the way they crafted their burial sites.  The Yamnaya spoke an early version of the Indo-European language, and brought it south to the future Greek, Paleo-Balkan, and Albian cultures.  They also moved east, across the Caucasus Mountains, and into Armenia, where their descendants still carry Yamnaya DNA today.  More puzzling, however, is another early group, the Anatolian, who spoke a language that shares key features with the Indo-European tongues, but does not appear to have been directly related to the Yamnaya.  This presented scientists with something of a mystery:  For the languages to have been related, these two peoples must have interacted closely and frequently, but that level of interaction should result in inter-breeding, which would leave some trace in their DNA.

Of course, obtaining DNA from ancient specimens isn’t exactly easy, especially in regions known for their excessive heat.  The strands can become damaged and unworkable, offering scientists little insight into the migration patterns of our ancestors, until another breakthrough in DNA analysis of archaeological remains that occurred in 2015.  DNA located in the petrous bone of the inner ear doesn’t decay at nearly the same rate, and can survive for thousands of years even in warm climates.  This realization enabled Iosif Lazaridus at Harvard University, along with a team of 206 archaeologists, linguists, and local historians spanning 30 countries, to analyze and compare the DNA of 777 people across the Southern Arc.  This includes parts of Croatia, modern-day Turkey, and Iran, a swath that runs from Europe proper into the Middle East.  The goal was to use this analysis to determine how these early cultures moved, mingled, and interacted with one another by tracking similarities and differences in their DNA.  The team found evidence of not one, but two different migrations that begins to explain the mystery of the shared linguistic roots between the Yamnaya and the Anatolian peoples.  Somewhere around 11,000 years ago, farmers from a region known as the Levant began populating the Southern Arc.  They were joined 4,000 to 6,000 years later by migrants from the Caucasus region.  Both the Yamnaya and the Anatolian cultures share some ancestry with these people from the South Caucasus, suggesting that the early Indo-European languages date much further back in time than we thought.  The two languages might have mixed in the highlands of West Asia, thousands of years before the Yanmaya migrated to other areas of the Southern Arc. In other words, the answer might be very simple: The roots of the Indo-European language go back much further than we believed, but so far we not been able to identify the earliest Anatolian population and more research needs to be done.  The goal is to find a “missing link” between the Eurasian Steppe and Anatolia to bind the languages of the regions together. As the authors describe it, the “discovery of such a ‘missing link’ … would end the centuries-old quest for a common source binding through language and some ancestry many of the peoples of Asia and Europe.”

Language, of course, doesn’t require DNA to change and evolve.  Human communication takes on a life of its own.  Two hearing impaired children will spontaneously invent their own proto-sign language without any training or instruction.  Two populations gathered together that speak different languages will create a workable middle ground known as a “creole” faster than anyone would think possible.  There are dozens of creole languages around the world, springing up almost whenever two cultures come into contact with one another. It is quite possible that shared languages do not mean shared DNA, something the authors are quick to point out, but it also seems beyond the realm of reasonableness that two peoples sharing the same space and speaking the same tongue would not form relationships and interbreed.  Language is critical to almost every human cooperative endeavor, but it’s never been a requirement for sexual relationships.  Love is sometimes called the “universal language” because affairs of the heart take precedence over speech, but with the exception of the Ashkenazi Jews there are very few instances where cohabitation and shared language do not lead to shared DNA.  It seems far more likely than not that these two populations must’ve shared a common ancestor and new techniques will enable us to discover it in the not-too-distant future.  There is one more caveat:  For simplicity’s sake, the team only analyzed the Y chromosome and their analysis only captures the male lineage.  It is possible that some piece of the picture is missing, but again it remains more than likely we are on our way to solving another key mystery in the origin of the human race and the beginnings of culture.  A story that we are increasingly learning is written right there in our DNA, we just need the tools to read it and the ability to understand it.

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